Methodology for quantitating uridine levels in plasma and tissues was developed and is being employed to elucidate the biochemical basis for the unique spectrum of antitumor activity exhibited by PALA (NSC-224131). X-ray crystallographic studies comparing structures of active and inactive analogues of m-AMSA (NSC-141549) were initiated in an attempt to relate crystal structure with antitumor activity. In a continuing study, alkaline sucrose gradient sedimentation experiments were conducted to determine the effects of m-AMSA on the integrity of cellular DNA. Several analogues of Actinomycin D were synthesized and analyzed for biological effects.